A dead KitchenAid Diamond Blender revived! (Part 1 of 2)

This is a documentation of what I did to investigate, diagnose, and eventually repair a dead blender. Below is Part One where I partially repaired it after some basic diagnostic checks. There was still a teething issue after this and I had to investigate further with more in-depth diagnostic techniques which I have documented in Part Two, where the steps leading to complete repair of the blender are explained.

Background: The blender is a KitchenAid Diamond Model 5KSB1585BAC and belongs to a friend. It has been in faithful service for about nine years before it just stopped working one day when in use. The power indicator LED did not even light up when power was switched on. So it was pretty much dead. I asked my friend to firstly check the fuse inside the power plug using a smartphone with this technique (cos she had no access to a multimeter) - https://www.youtube.com/watch?v=HGbHekFFuLg. The fuse was deemed ok and she removed the bottom of the blender in order to inspect the components inside. The base was simple to detach by simply removing four screws (two were partially hidden by rubber feet that popped out easily). A quick visual inspection of the insides didn't reveal any obvious signs of damage. So I took over the blender to diagnose further.


The first thing I did was to check the large rectangular metallic component (seen on the right side of the image above) for electrical continuity.

That component connects the mains AC inlet wires and then outputs power to the circuit board. I found out from the label on the component that it is an EMI filter, which is basically an assembly of capacitors and inductors across the power lines to filter out unwanted electrical noise signals. My thought was that perhaps it was damaged internally and so couldn't pass the AC power out to the circuit board. So I used a multimeter to check for continuity and it turned out to be good.

I even confirmed that it was able to output AC230V when I power up the 3-pin plug.

Next, I wanted to know if the motor was good. I was able to find this label pasted on the motor and it indicated it was an AC motor running on an AC voltage level that's the same as the mains voltage (i.e. 230V). It also rates the motor at 660W. Quite a beast of a motor for a blender! Typically, motors used in home appliances like blenders, fans, and vacuum cleaners are AC motors, which are brushless. This means that it is fairly easy to detect a damaged motor coil by simply checking for electrical continuity at the motor terminals (whereas in brushed DC motors, there are other possible reasons such as worn out brushes or a damaged commutator that can contribute to failed electrical continuity across the motor terminals). I unplugged the motor from the circuit board and did the continuity test like this -



If the electrical continuity test on the AC motor had failed, I would have had to remove the motor to look for what is known as a thermal fuse connected to it which could have blown (due to overheating) or if the problem was caused by a burnt wire somewhere in the motor's wire coil. Replacing a blown thermal fuse could be easy or hard depending on where it is embedded. But a burnt motor coil would mean there's no way to repair the mote and at the point, it would be time to search for a replacement motor and it could be the most expensive spare part of the appliance. So thankfully this wasn't the case. It was also not easy to detach the motor from this blender after I tried to, so I was glad to be spared of this ordeal.

Moving on, the only thing left for me to investigate was the circuit board.
At this juncture, I was quite convinced that the electronics is the problem and there are only two possible ways to successfully repair this blender-
1. The exact electronic component(s) on the circuit board that is(are) faulty can be found and can be replaced.
2. Purchasing the entire circuit board assembly as a spare part to replace it.

I unplugged the motor cables, the power supply cables (coming from the EMI filter, the large metal box component I test earlier) before trying to remove the control panel assembly. I also had to detach a small black component (no marking on it) held in place by magnet forces under the fan of the motor, as it is permanently secured to the circuit board. I suspected it could be some kind of hall sensor to check for the rotation of the motor.

It was tricky removing the whole control panel assembly as the motor was getting in the way, but after some careful prying, the entire assembly (which included the button panel) was detached.

A few screws had to be removed to separate the plastic housing, and then two distinct circuit boards can be seen - one for the power electronics and the other for the control panel electronics, both linked to each other by five exposed and uninsulated wires.


I wasn't able to see any damaged component on the boards at first, but upon closer inspection at the back of the boards, I noticed some kind of burnt mark and it seemed like something has dropped away from the board due to the burnt.

Using a magnifier app on my phone to zoom in really close, it became clear that the missing part that had been burnt off was not a component, but a small section of the copper trace!

I have never encountered such a fault before, but it was good news because all I needed to do was to bridge the broken trace with a piece of wire.

So I soldered a suitable wire across two existing solder points found on each side of the broken trace and then quickly assembled the circuit boards back into the blender and proceeded to test the blender immediately.

I was very excited that the power indicator LED lit up when I pressed the power button!  And then I pressed the various mode buttons and they all seemed to be working too. Hooray! I thought it was a success.... but my excitement was short-lived (watch the video below to see what happened at the end of the test). :P

The blender tripped my home's main circuit breaker whenever it got powered off. Even when trying out the pulse mode or the ice crushing mode, where the motor has to stop temporarily, it would trip my home's circuit breaker too. Dang!

It wasn't a repair success at this point but at least I confirmed that the motor is still working well and the control panel are in good order. What could be causing the power trip? I continue in Part Two of the repair, where further in-depth diagnostics were made, with some interesting suggestions from friends at Repair Kopitiam, a local community of repair enthusiasts. Head over to Part Two now!